Dragging working set item past top/bottom ends drag

[njx]

1. Open a few files in the working set
2. Start dragging one of the filenames upward
3. Drag it past the top of the list and then back down

Result: After it hits the top of the list, the item is no longer dragged, even though the mouse is still down.

[njx]

Low pri to @jasonsanjose - I don't remember who merged the dragging PR (I think it was a community submission); feel free to reassign.

[peterflynn]

Might be fixed by #4920... I should be able to put up a pull request for that soon

[peterflynn]

FBNC @njx now that PR #7820 has landed

[njx]

Yup, works well now (except for the autoscroll issue). Closing.